Brunel signs deal to develop “air hybrid” system for buses

Novel start-stop technology relies on regenerative braking and compressed air

Brunel University has signed a licensing deal with a major manufacturer in China that could see a stop-start engine system that relies on compressed air installed in buses across the country.  

The deal is between Brunel and Guangxi Yuchai Machinery Company, said to be China’s largest diesel engine manufacturer, supplying some 70% of bus engines in the country.

The Brunel-Yuchai team is currently developing a prototype of the “air hybrid” system, which captures and stores braking energy as compressed air during braking using a device commonly installed in heavy goods vehicles. The stored compressed air can then be used to restart the engine through an air starter motor. It means the bus can turn off its engine when stationary and then restart it using energy captured from regenerative braking, leading to significant fuel and cost savings, the developers of the technology said.

A demonstration vehicle is to be built to highlight the economic and environmental benefits to Chinese bus operators. It is thought the system could then be mass-produced.

Jie Shen, chief engineer at Guangxi Yuchai Machinery Company, said: “This air hybrid engine technology is the most cost-effective fuel saving technology for city buses in China. We will work hard to ensure that it will be implemented in production in the near future.”

Installing the system on China’s buses would lower fuel consumption and reduce pollution. The technology is also attracting interest from parties in the US and India.

It is based on novel regenerative engine braking stop-start technology developed by academics at Brunel’s Centre for Advanced Powertrain and Fuels.

The technology is compatible with existing vehicle powertrain systems and is designed to be more efficient than an electric stop-start system. The production cost is also said to be significantly lower, making it suitable for high volume production.

The air hybrid system is expected to produce a 10% benefit in fuel economy when installed on a city bus.